Drying units are used in offset printing machines to dry and/or cure the ink or varnish which is applied to the sheet or web material. One such dryer unit is disclosed in EP 0 035 741 Bl. Specifically, this reference discloses a sliding table having a cooling surface which is arranged opposite a dryer device. The sliding table acts as a printed material guide system and is arranged with its cooling surface facing the unprinted side of the printed material. In order to dry the printed material, which is described as a thermoplastic sheet material, the dryer device blows air in the direction of the cooling surface. The printed material guide system further includes coolant ducts which are connected to a cooling system comprising a heat exchanger and circulating pump.
A deliverer in a sheet-fed printing machine which has dryer devices arranged in a modular construction within the chain conveyor system is disclosed in PCT/WO 95-01930. Air assisted printed material guide systems are arranged opposite the dryer devices and underneath the sheet conveying path.
Another dryer unit is disclosed in DE 92 14 459 Ul. This particular dryer unit is constructed with a cooling system which includes a heat exchanger, a flow monitor, a compensation container and a circulation pump. The cooling system further includes a coolant line interconnecting the circulation pump and a sheet guide plate which provides coolant to the sheet guide plate. In addition, the coolant outlet of the sheet guide plate can be coupled by means of a connecting line to a dryer unit positioned opposite the sheet guide plate in order to also provide coolant to the dryer unit. The cooling of the dryer unit and the sheet guide plate prevents heat from building up within the printing machine. In order to accelerate the oxidative drying of the printing inks, the printed material itself is heated by means of infrared radiation.
DE 43 08 276 Al also discloses a sheet guide device having a cooling device which cools the sheet guide surface when a dryer unit is operating. The sheet guide surface has a plurality of openings through which air is blown. One of the openings is formed by an end face integrated in the sheet guide surface as an impact face and includes a flow duct which opens at an angle into the sheet guide surface. The cooling device is configured as a cooling trough having a trough bottom and a lid wherein the lid of the trough constitutes the sheet guide plate.
One of the significant problems with these designs is that the dryer units are always arranged opposite the printed material guide system. Thus, the printed material is dried only from one side (the front side). This leads to problems in the drying process including, for example, smearing (setting-off) of the ink and/or varnish which resulting from inadequately dried printed materials reaching the deliverer stack.
A drying device for printed products which is arranged to dry both the front and rear side of the printed material is disclosed in DE 38 28 753 C2. The drying device includes an energy transmission device comprising a fiber optic cable and a rectilinearly fanned-out beam splitter device. The drying device is arranged on both sides of printed material in the sheet deliverer, however, and is not integrated with a sheet guide system.